1. Field of the Invention
The present invention relates to tantalum chip capacitors. More particularly, though not exclusively, the present invention relates to improved tantalum chip capacitors and methods for manufacturing the same.
2. Problem in the Art
Capacitors exist in the art which are made from a capacitive element such as a tantalum slug or pellet. To create a conventional tantalum slug, tantalum powder is pressed with a binder and then exposed to a process for forming a polarized capacitor having a positive end and a negative end. A typical tantalum slug will have an anode comprised of a wire extending from the slug and a cathode comprised of a conductive surface formed at the opposite side of the tantalum slug.
Some prior art tantalum capacitors are formed by cutting the anode wire and covering the anode and cathode ends of the capacitor with a conductive material. This results in a nib or bump that sticks out of the package, increasing the size and non-uniformity of the part. The electrical contact between the tantalum wire and the conductive material is through the sides of the tantalum wire, therefore requiring this nib.
Other prior art tantalum slugs are fitted with external leads which are comprised of discrete pieces of metal attached to the anode and cathode of the capacitive element. Users of such tantalum capacitors desire to attach the capacitors to a circuit board using reflow solder. As a result, terminations are required which are suitable to be attached to a circuit board using reflow solder. Prior art tantalum capacitors fitted with such external leads have been produced in various ways. Some prior art capacitors are made using a lead frame providing connection terminals where the tantalum slug is placed within a lead frame. An electrical connection is made between the anode and cathode and one of the connection terminals. Other prior art tantalum capacitors use a flat metal piece which is directly connected to the anode lead of the tantalum slug. The excess portions of the anode leads can be sheared off so that the flat metal piece provides a surface for use as an anode terminal. Other prior art tantalum slugs are disposed within metal channels which form anode and cathode terminals. The anode lead wire of the tantalum slug can be welded to the metal channel to form an electrical connection. Other prior art tantalum slugs simply have discrete metal terminals which are fixed to the ends of the tantalum slug and which make electrical contact to the anodes and cathodes of the tantalum slug. Still other prior art tantalum slugs are processed with a flat piece of tantalum metal being substituted for the tantalum wire at the anode end, and with a similar flat piece of metal being attached to the opposing cathode end, and with both pieces of metal being further metallized on their external faces so as to provide solderable surfaces.
It is known in other fields of technology to use thin film metallization methods such as sputtering to coat the ends of devices such as chip resistors.
It can therefore be seen that there is a need for an improved tantalum chip capacitor and method for making the same.